A variety of fluid operated clutch control systems for controlling engagement and disengagement of the vehicle master friction clutch between a driver member and driven member, such as a vehicular engine and change gear transmission, have been developed over past years. Early examples of such systems are disclosed in U.S. Pat. No(s). 1,317,029; 2,137,961; 2,137,939 and more recent examples of such systems are disclosed in U.S. Pat. No(s). 3,548,981; 3,719,102; 3,799,309; 4,236,617 and 4,448,293, the disclosures of all of which are incorporated herein by reference.
Locking mechanisms have been employed to a lesser extent in the past to lock vehicle components in selected positions upon the occurrence of one or more predetermined conditions such as the pressure actuated ratchet used in the air brake control system disclosed in U.S. Pat. No. 2,099,453; the fluid actuated latch used in the power shifting mechanism disclosed in U.S. Pat. No. 2,180,154; the ratchet member used in the power system for operating control members disclosed in U.S. Pat. No. 2,932,282, and the latch member used in the automatic clutch control system disclosed in U.S. Pat. No. 4,729,462, the disclosure of all which are incorporated herein by reference and the last of which is owned by the assignee of the present invention.
As disclosed in the above described prior art, the latch members have characteristically been devices that engage external members of the control system whereas the present invention provides a latching member that is operable to enter directly into the fluid chamber containing the pressurized fluid that controls the clutch condition and is thus advantageously effective in locking the clutch in a preselected condition when the fluid pressure is below a predetermined minimum value so as, for example, to prevent the engine from driving the transmission when for some reason the fluid pressure has dropped below the predetermined minimum value and the vehicle is traveling at low speed or alternately, to prevent the engine from disengaging from the transmission to assure engine braking when the vehicle is decending a hill.